1. Field of the Invention
The present invention relates generally to a pressure sensor and, in particular but not exclusively, to a pressure sensor for detecting the pressure of oil for use in controlling, for example, an automobile transmission.
2. Description of the Related Art
FIGS. 1 and 2 depict a conventional pressure sensor for detecting the pressure of a gas or fluid medium, and are exemplary of the various types of pressure sensors that have been proposed. This pressure sensor A houses a sensor unit 2 for converting the pressure of the fluid medium to an electrical signal in a housing 1, and has a pressure inlet tube 3 for introducing the fluid medium to the sensor unit 2. The sensor unit 2 has a sensor chip formed of a semiconductor substrate and including a thin-film diaphragm (not shown) and a detector element (piezoresistor, for example) for detecting pressure-induced distortion of this diaphragm. The housing 1 includes a generally box-shaped body 1a and a cover 1b both made of a synthetic resin. The body 1a has a metal pressure inlet tube 3 in the form of a substantially cylindrical shape insert-molded to project from the bottom thereof. A plurality of pins 4 for supplying an electrical signal from the sensor unit 2 to an external device are implanted in the body 1a, and the ends of these pins 4 are connected to the sensor unit 2 by means of wires 6, which are made of a conductor such as gold or aluminum.
The sensor unit 2 is attached to the end of the pressure inlet tube 3 by means of a glass seat 5, and the pressure of the fluid medium is introduced from an external source through the pressure inlet tube 3 to the diaphragm of the sensor unit 2. The plural pins 4 project in two directions from both sides of the housing 1 to facilitate mounting to a printed circuit board.
One application for the pressure sensor A as described is for oil pressure detection in the control of an automatic transmission of an automobile. In such application, oil pressure is repeatedly applied and then released, and in the course of this a momentarily high pressure surge can occur. The problem is that when the surge pressure exceeds the breakdown strength of the sensor unit 2, the sensor unit 2 can be destroyed.